Flame-retardant resin composition and flame-retardant resin molded article

ABSTRACT

To improve the thermal stability of a brominated polymer type flame retardant in a flame-retardant resin composition containing a styrene-based resin and the brominated polymer type flame retardant to provide a flame-retardant resin molded article in which occurrences of black foreign substances and discoloration decrease 
     The flame-retardant resin composition contains a styrene-based resin, a brominated polymer type flame retardant, an epoxy compound, and a halogen capture agent, wherein a content of bromine is 18 to 42% by mass.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a flame-retardant resin composition containing a styrene-based resin and a brominated polymer type flame retardant, and a flame-retardant resin molded article using the flame-retardant resin composition.

Description of Related Art

Hexabromocyclododecane (HBCD) has been generally used as a flame retardant used for imparting flame retardancy to a styrene-based resin molded article. Since HBCD has a bioaccumulation property, is toxic for aquatic organisms, and is hardly decomposed, a brominated polymer type flame retardant is considered as a substitute (see Patent Literature 1).

However, the brominated polymer type flame retardant has insufficient thermal stability, and is thermally deteriorated to cause black foreign substances or discoloration when the brominated polymer type flame retardant is exposed to a high temperature in a process for mixing the brominated polymer type flame retardant with a styrene-based resin to manufacture a flame-retardant resin composition, and a molding process for molding a flame-retardant resin molded article using the flame-retardant resin composition. This may impair the appearance of the molded article.

Patent Literature 2 discloses a technique of adding an alkyl phosphite or an epoxy compound as a stabilizer when a brominated polymer type flame retardant is mixed with a resin as a method for eliminating the occurrence of such black foreign substances.

PRIOR ART REFERENCE Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2009-516019

Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2012-512942

BRIEF SUMMARY OF THE INVENTION Problem to be Solved by the Invention

An object of the present invention is to provide a flame-retardant resin composition containing a styrene-based resin and a brominated polymer type flame retardant, and a flame-retardant resin molded article.

Means for Solving the Problem

A first aspect of the present invention is a flame-retardant resin composition characterized by containing a styrene-based resin and a brominated polymer type flame retardant, an epoxy compound, and a halogen capture agent, wherein a content of bromine is 18 to 42% by mass.

A flame-retardant resin composition of the present invention contains the following preferred aspects: the flame-retardant resin composition contains 4 to 25 parts by mass of the epoxy compound and 0.8 to 15 parts by mass of the halogen capture agent based on a total of 100 parts by mass of the styrene-based resin and brominated polymer type flame retardant; the halogen capture agent contains at least a dolomite-based compound and a hydrotalcite-based compound; a mass ratio of the dolomite-based compound to the hydrotalcite-based compound (dolomite-based compound/hydrotalcite-based compound) is 10/90 to 90/10; the flame-retardant resin composition further contains an antioxidant; the antioxidant is a hindered phenol-based antioxidant; and the flame-retardant resin composition contains 0.8 to 7 parts by mass of the antioxidant based on a total of 100 parts by mass of the styrene-based resin and brominated polymer type flame retardant.

A second aspect of the present invention is a flame-retardant resin molded article characterized by containing the flame-retardant resin composition of the first aspect of the present invention.

Furthermore, a third aspect of the present invention is a flame-retardant resin molded article characterized by containing the flame-retardant resin composition of the first aspect of the present invention and a further styrene-based resin.

Effects of the Invention

The present invention can provide a flame-retardant resin composition in which the thermal stability of a brominated polymer type flame retardant is improved by using an epoxy compound and a halogen capture agent in combination as a stabilizer of the brominated polymer type flame retardant. Therefore, the occurrence of black foreign substances when a molded article is obtained by molding the flame-retardant resin composition of the present invention is reduced, which provides a flame-retardant resin molded article having excellent appearance.

The present invention uses the dolomite-based compound and the hydrotalcite-based compound in combination as the halogen capture agent, which provides the flame-retardant resin composition in which the thermal stability of the brominated polymer type flame retardant is further improved, and the flame-retardant resin molded article reducing the occurrence of black foreign substances, preventing the occurrence of discoloration, and having excellent appearance.

The present invention uses the antioxidant in addition to the epoxy compound and the halogen capture agent, which provides a flame-retardant resin composition in which the thermal stability of the brominated polymer type flame retardant is further improved, and a flame-retardant resin molded article preventing the occurrence of black foreign substances, suppressing the occurrence of discoloration, and having excellent appearance.

Furthermore, the present invention uses the dolomite-based compound and the hydrotalcite-based compound in combination as the halogen capture agent, and uses the antioxidant in combination, which provides a flame-retardant resin composition in which the thermal stability of the brominated polymer type flame retardant is highly unproved, and a flame-retardant resin molded article preventing both the occurrence of black foreign substances and the occurrence of discoloration, and having excellent appearance.

DETAILED DESCRIPTION OF THE INVENTION Mode for Carrying Out the Invention

A flame-retardant resin composition of the present invention (hereinafter referred to as a “resin composition”) is characterized by using an epoxy compound and a halogen capture agent in combination as a heat stabilizer for a brominated polymer type flame retardant blended in a styrene-based resin, and a flame-retardant resin molded article of the present invention is obtained by molding the resin composition. The flame-retardant resin molded article of the present invention may be a flame-retardant resin molded article (hereinafter referred to as a “first molded article”) obtained by molding the resin composition of the present invention as it is, or a flame-retardant resin molded article (hereinafter referred to as a “second molded article”) in which a styrene-based resin is further added to the resin composition of the present invention to adjust the content of bromine to a lower level.

Hereinafter, the resin composition of the present invention, and the first and second molded articles will be described in detail.

Examples of the styrene-based resin used for the resin composition of the present invention include a homopolymer of styrene, a copolymer of styrene and copolymerizable monomer, and rubber-reinforced styrene-based resins thereof. Examples thereof include polystyrene, rubber reinforced polystyrene (HIPS), acrylonitrile-styrene copolymer resin (AS), acrylonitrile-butadiene-styrene copolymer resin (ABS), acrylonitrile-acrylic rubber-styrene copolymer resin (AAS), acrylonitrile-ethylene propylene rubber-styrene copolymer resin, acrylonitrile-chlorinated polyethylene-styrene copolymer resin, and styrene-butadiene copolymer resin. These styrene-based resins may be used singly or two or more of them may be used at the same time. Most preferred is polystyrene.

The brominated polymer type flame retardant used for the present invention is conventionally known, and those disclosed in Patent Literatures 1 and 2 can be used as they are. Preferably, a brominated copolymer having the following features (a) to (f) is preferably used:

(a) the brominated copolymer is a copolymer having butadiene and vinyl aromatic hydrocarbon as a monomer component;

(b) the content of the vinyl aromatic hydrocarbon monomer in the copolymer before bromination is 5 to 90% by mass;

(c) 1,2-butadiene is contained in butadiene; and

(d) the weight average molecular weight (Mw) is 1000 or more;

(e) the content of unbrominated nonaromatic double bonds determined by ¹H-NMR spectroscopy is less than 50% based on the content of the nonaromatic double bonds of the copolymer before bromination; and

(f) the 5% weight reduction temperature obtained by thermogravimetric analysis (TGA) is 200° C. or higher.

Among them, examples thereof include a brominated styrene-butadiene block copolymer, a brominated styrene-butadiene random copolymer, and a brominated styrene-butadiene graft copolymer, which have the above features (a) to (f) and in which the vinyl aromatic hydrocarbon is styrene. In particular, a brominated styrene-butadiene block copolymer is preferred, and specific examples thereof include commercially available products such as “EMERALD INNOVATION 3000” manufactured by Chemtura Corporation and “FR 122 P” manufactured by ICL Company.

In the present invention, the addition amount of the brominated polymer type flame retardant is adjusted so that the content of bromine in the resin composition is 18 to 42% by mass.

Examples of the epoxy compound used in the present invention include a cresol novolac type epoxy resin, a phenol novolac type epoxy resin, and an epoxidized vegetable oil. These can be used alone or in combination of two or more kinds. Among these, the cresol novolac type epoxy resin and the epoxidized soybean oil are preferable. The addition amount of the epoxy compound is preferably 4 to 25 parts by mass with respect to a total of 100 parts by mass of the styrene-based resin and brominated polymer type flame retardant. This range makes it possible to improve the thermal stability of the brominated polymer type flame retardant, to effectively suppress the occurrence of black foreign substances due to the thermal deterioration of the brominated polymer type flame retardant in the resin composition, and the first molded article and the second molded article using the resin composition, and to provide a molded article having excellent molding processability and excellent appearance. More preferred is 10 to 20 parts by mass.

The halogen capture agent used for the present invention is a component which captures free halogen produced during a process until the first molded article or the second molded article is obtained from the manufacturing process of the resin composition. Examples thereof include a dolomite-based compound, a hydrotalcite-based compound, a magnesium perchlorate compound, an aluminosilicate compound (zeolite or the like), and an organotin compound. Among them, the dolomite-based compound and the hydrotalcite-based compound are preferable. The hydrotalcite-based compound is one kind of naturally produced clay minerals represented by Mg₆Al₂(OH)₁₆CO₃.nH₂O or the like. These halogen capture agents may be used singly or as mixtures of two or more.

The addition amount of the halogen capture agent is preferably 0.8 to 1.5 parts by mass with respect to a total of 100 parts by mass of the styrene-based resin and brominated polymer type flame retardant. This range makes it possible to improve the thermal stability of the brominated polymer type flame retardant, to effectively suppress the occurrence of black foreign substances due to the thermal deterioration of the brominated polymer type flame retardant in the resin composition, and the first molded article and the second molded article using the resin composition, and to provide a molded article having excellent molding processability and excellent appearance. More preferred is 5 to 10 parts by mass.

The present invention uses the dolomite-based compound and the hydrotalcite-based compound in combination as the halogen capture agent to make it possible to prevent the occurrence of discoloration and to reduce the occurrence of black foreign substances. In this case, the mass ratio of the dolomite-based compound to the hydrotalcite-based compound (dolomite-based compound/hydrotalcite-based compound) is preferably 10/90 to 90/10. In such a range, the thermal stability of the brominated polymer type flame retardant is satisfactorily improved. The occurrence of discoloration due to thermal deterioration of the brominated polymer type flame retardant is effectively prevented in the resin composition, and the first molded article and the second molded article using the resin composition, which provides a molded article having excellent appearance. The mass ratio (dolomite-based compound/hydrotalcite-based compound) is more preferably 30/70 to 70/30.

When the dolomite-based compound and the hydrotalcite-based compound are used in combination, a magnesium perchlorate compound, an aluminosilicate compound (such as zeolite), and an organotin compound or the like may be used in combination in addition to these compounds. However, it is preferable to use only the dolomite-based compound and the hydrotalcite-based compound.

The present invention further uses an antioxidant in addition to the epoxy compound and the halogen capture agent as the heat stabilizer of the brominated polymer type flame retardant, which makes it possible to prevent the occurrence of black foreign substances and to suppress the occurrence of discoloration.

Examples of the antioxidant used for the present invention include a phenol-based antioxidant, a sulfur-based antioxidant, and a phosphorus-based antioxidant. Preferred is a phenol-based antioxidant, and particularly preferred is a hindered phenol-based antioxidant. Examples of the hindered phenol-based antioxidant include octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, ethylenebis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], 4,6-bis(octylthiomethyl)-o-cresol, 4,6-bis[(dodecylthio)methyl]-o-cresol, 2,4-dimethyl-6-(1-methylpentadecyl)phenol, tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane, DL-α-tocopherol, 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate, 4,4′-thiobis(6-tert-butyl-3-methylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, and 4,4′-butylidenebis(3-methyl-6-tert-butylphenol). Among them, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate is most preferred.

The addition amount of the antioxidant is preferably 0.8 to 7 parts by mass with respect to a total of 100 parts by mass of the styrene-based resin and brominated polymer type flame retardant. This range makes it possible to improve the thermal stability of the brominated polymer type flame retardant in the resin composition, to effectively suppress the occurrence of black foreign substances due to the thermal deterioration of the brominated polymer type flame retardant in the first molded article and the second molded article, to effectively suppress the occurrence of discoloration, and to provide a molded article having excellent appearance.

In the present invention, by using the dolomite-based compound and the hydrotalcite-based compound in combination as the halogen capture agent and further using the antioxidant, the thermal stability of the brominated polymer type flame retardant is more effectively improved. The occurrence of black foreign substances and the occurrence of discoloration due to the thermal deterioration of the brominated polymer type flame retardant are simultaneously prevented, and a molded article having excellent appearance can be obtained.

Other additives can be added to the resin composition of the present invention as long as the effects of the present invention are not impaired. Examples thereof include: lubricants such as fatty acid-based lubricants, aliphatic amide-based lubricants, and metal soap-based lubricants; fillers such as talc, mica, and silica; reinforcing agents such as glass fibers; coloring agents such as pigments and dyes; flame-retardant auxiliary agents such as antimony trioxide; and antistatic agents such as nonionic surfactants and cationic surfactants.

The resin composition of the present invention can be manufactured by previously blending a styrene-based resin, a brominated polymer type flame retardant, an epoxy compound, a halogen capture agent, and an antioxidant if necessary according to a known mixing technique to obtain a blended product, and thereafter melt-kneading the blended product. A preliminary blending method can be performed by using a mixer such as a mixer type mixing machine, a V type blender, or a tumbler type mixing machine or the like. The melt-kneading method is not particularly limited, and a known melting technique can be applied. Suitable examples of a melt-kneading apparatus used far melt-kneading include a uniaxial extruder, a special uniaxial extruder, and a biaxial extruder, and preferred is a biaxial extruder.

The resin composition of the present invention may be molded into the first molded article using the resin composition itself. However, by adding a further styrene-based resin (second styrene-based resin) to the resin composition of the present invention, a second molded article having a lower content of bromine can also be obtained. Also in this case, the thermal stability of the brominated polymer type flame retardant is well maintained; the occurrence of black foreign substances or yellow discoloration is suppressed or prevented; and a molded article having excellent appearance is obtained. As the second styrene-based resin, a styrene-based resin exemplified as a styrene-based resin (hereinafter referred to as a “first styrene-based resin”) used for manufacturing the above-described resin composition of the present invention is used. Preferably, the same styrene-based resin as the first styrene-based resin is used.

The resin composition of the present invention and the second styrene-based resin may be melt-kneaded to previously produce a second resin composition, followed by molding the second resin composition to obtain the second molded article. The resin composition of the present invention and the second styrene-based resin may be charged into a molding machine where the second molded article is directly obtained. When the second resin composition is previously produced, the melt-kneading apparatus is preferably used.

A method for molding the first molded article and the second molded article using the resin composition of the present invention is not limited. A method conventionally used for molding the flame-retardant resin molded article is suitably used. Extrusion molding is preferable, and preferably used for extrusion foam molding of a plate extruded foam. The plate extruded foam can be manufactured, for example, by blending the constituents of the resin composition and heating and melting the blended product, or heating and melting the previously produced resin composition, injecting a foaming agent at an arbitrary stage, followed by kneading to obtain a kneaded product, and adjusting the kneaded product to a foaming optimum temperature, and extruding and foaming the kneaded product in low pressure atmosphere (normal atmospheric pressure). A pressure when the foaming agent is injected is not particularly limited, and the foaming agent may not be gasified under a pressure higher than the internal pressure of an extruder or the like. When the plate extruded foam is manufactured, inorganic fillers such as silica, talc, and calcium carbonate can be used as a foam nucleating agent, if necessary. The density, foaming ratio, and average bubble diameter of the foam can be changed by adjusting the amount of the foaming agent or the amount of the foam nucleating agent. As the foaming agent, known ones such as lower hydrocarbons (such as propane, butane, pentane, and hexane); ethers (such as dimethyl ether and diethyl ether); ketones (such as dimethyl ketone and methyl ethyl ketone); alcohols such as methanol, ethanol, and propyl alcohol; halogenated hydrocarbons (such as trichloromonofluoromethane and methyl chloride); and inorganic gases (such as carbon dioxide gas and water) can be used each alone or as mixtures thereof. It is preferable to use lower hydrocarbons as a main component.

EXAMPLES

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

[Styrene-Based Resin]

A styrene homopolymer (polystyrene) was used, which had a weight average molecular weight (Mw) of 200,000 and a methanol soluble component amount of 1.2% by mass. The weight average molecular weight (Mw) and the methanol soluble component amount were measured by the following methods.

<Measurement of Weight Average Molecular Weight (Mw)>

Measurement was carried out using gel permeation chromatography (GPC) under the following conditions.

GPC model: “Shodex GPC-101” manufactured by Showa Denko KK

Column: “PLgel 10 μm MIXED-C” manufactured by Polymer Laboratories Co., Ltd

Mobile phase: chloroform

Sample concentration: 0.2% by mass

Temperature: 40° C. (oven)

Detector: differential refractometer

The molecular weight of each component in the present invention is obtained by calculating a molecular weight at each elution time from the elution curve of monodisperse polystyrene and calculating a molecular weight in terms of polystyrene.

<Measurement of Methanol Soluble Component Amount>

1 g of a sample was dissolved in 40 ml of a solvent (methyl ethyl ketone), and polystyrene was reprecipitated with 400 ml of a 10-fold amount of a poor solvent (methanol) to determine the mass of reprecipitated polystyrene, and the residue was taken as the methanol soluble component amount.

[Brominated Polymer Type Flame Retardant]

“EMERALD INNOVATION 3000” (a brominated styrene-butadiene block copolymer having the above features (a) to (f), content of bromine: 60% by mass) manufactured by Chemtura Corporation

[Epoxy Compound]

Epoxy compound-1 “ARALDITE (registered trademark) ECN 1280” (cresol novolac type epoxy resin) manufactured by Huntsman Japan Co., Ltd.

Epoxy Compound-2: “New Sizer 510R” (epoxidized soybean oil) manufactured by NOF CORPORATION

[Halogen Capture Agent]

Halogen capture agent-1: “PLENLIZER HC-100B” (dolomite-based compound) manufactured by Ajinomoto Fine-Techno Co.

Halogen Capture Agent-2: “MC-63A” (hydrotalcite-based compound) manufactured by Nitto Kasei Co., Ltd.

[Antioxidant]

Antioxidant: “Irganox 1076” (octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) manufactured by BASF Japan

Examples 1 to 8 and Comparative Examples 1 and 2

Components were charged into a mixer in blended amounts shown in Table 1, for preliminary blending. The blended product was supplied to a biaxial extruder (“TEM 26SS: 14 barrel” manufactured by Toshiba Corporation) using a metering feeder, and melt-kneaded and extruded under extrusion conditions of a cylinder temperature of 180° C., a total feed rate of 30 kg/hour, and a screw rotation speed of 300 rpm. The extruded strand was water-cooled and then led to a pelletizer to obtain resin composition pellets. No black foreign substances occurred in any of the obtained pellets. The content of bromine in the obtained resin composition pellets was measured by the following method, and the following thermal stability was evaluated. The results are shown in Table 1.

[Method for Measuring Content of Bromine]

The content of bromine in the resin composition pellets was measured by combustion-ion chromatography under the following conditions.

Model: “AQF-100” manufactured by Mitsubishi Chemical Corporation and “DX-120” manufactured by Dionex Corporation

Combustion tube temperature: 1000° C.

Detector: Electrical conductivity detector

Column: AS 12A

Flow rate: 1.5 ml/min

Eluent composition: 2.7 mM Na₂CO₃+0.3 mM NaHCO₃

Sample introduction amount: 5 μl

Sample amount: 3 mg

[Evaluation of Thermal Stability]

10 g of the resin composition pellets were weighed, placed in a glass bottle, heated in a gear oven at 220° C. for 60 minutes, taken out, and cooled. After completely cooling, the occurrence state of black foreign substances was visually observed, and evaluated according to the following criteria.

Good: 4 or less black foreign substances occurred.

Poor: 5 or more black foreign substances occurred.

TABLE 1 Comparative Examples Examples 1 2 3 4 5 6 7 8 1 2 Styrene-based resin + 100  100  100  100  100  100  100  100  100  100  brominated polymer type flame retardant (parts by mass) Epoxy compound-1 (parts by mass) 10  10  10  10  — 10  5 22  — 10  Epoxy compound-2 (parts by mass) 5 — — 5 10  5 — — — 5 Halogen capture agent-1 (parts by mass) 6 6 6 1 — 12  12  6 6 — Halogen capture agent-2 (parts by mass) — — — — 6 — — — — — Content of bromine in composition 30  20  40  30  30  30  30  30  30  30  (% by mass) Evaluation of heat stability Good Good Good Good Good Good Good Good Poor Poor

Examples 9 to 18 and Comparative Examples 3 and 4

Resin composition pellets were obtained in the same manner as in Example 1 except that the blending amount of each component was changed to the blending amount shown in Table 2. No black foreign substances or discoloration occurred in any of the obtained pellets. The content of bromine in the obtained resin composition pellets was measured in the same manner as in Example 1, and the thermal stability was evaluated in the same manner as in Example 1. In the evaluation of the thermal stability, the occurrence state of discoloration was also visually observed. The evaluation criteria are as follows. The results are shown in Table 2.

the occurrence state of black foreign substances

Good: 4 or less black foreign substances occurred

Poor: 5 or more black foreign substances occurred.

the occurrence state of discoloration

Good: No discoloration occurred.

Poor: Obvious discoloration occurred.

TABLE 2 Comparative Examples Examples 9 10 11 12 13 14 15 16 17 18 3 4 Styrene-based resin + 100  100  100  100  100  100  100  100  100  100  100  100  brominated polymer type flame retardant (parts by mass) Epoxy compound-1 (parts by 10  10  10  10  — 10  10  5 22  — — 10  mass) Epoxy compound-2 (parts by 5 — — 5 10  5 5 — — 22  — 5 mass) Halogen capture agent-1 (parts 5 5 5   0.5 7 1 9 5 5 5 5 — by mass) Halogen capture agent-2 (parts 5 5 5   0.5 7 9 1 5 5 5 5 — by mass) Mass ratio of halogen capture 50/50 50/50 50/50 50/50 50/50 10/90 90/10 50/50 50/50 50/50 50/50 — agent (capture agent-1/ capture agent-2) Content of bromine in 30  20  40  30  30  30  30  30  30  30  30  30  composition (% by mass) Evaluation of Black foreign Good Good Good Good Good Good Good Good Good Good Poor Poor heat stability substance Discoloration Good Good Good Good Good Good Good Good Good Good Poor Poor

Examples 19 to 29 and Comparative Examples 5 and 6

Resin composition pellets were obtained in the same manner as in Example 1 except that the blending amount of each component was changed to the blending amount shown in Table 3. No black foreign substances or discoloration occurred in any of the obtained pellets. The content of bromine in the obtained resin composition pellets was measured in the same manner as in Example 1, and the thermal stability was evaluated in the same manner as in Example 1. In the evaluation of the thermal stability, the occurrence state of discoloration was also visually observed. The evaluation criteria are as follows. The results are shown in Table 3.

the occurrence state of black foreign substances

Good: No black foreign substances occurred.

Poor: Black foreign substances occurred.

the occurrence state of discoloration

Good: No discoloration occurred.

Average: Discoloration slightly occurred.

Poor: Obvious discoloration occurred.

TABLE 3 Examples 19 20 21 22 23 24 25 Styrene-based resin + 100  100  100  100  100  100  100  brominated polymer type flame retardant (parts by mass) Epoxy compound-1 (parts by mass) 10  10  10  10  10  5 22  Epoxy compound-2 (parts by mass) 5 — — 5 5 — — Halogen capture agent-1 (parts by mass) 5 5 5   0.5 7 5 5 Halogen capture agent-2 (parts by mass) 5 5 5   0.5 7 5 5 Mass ratio of halogen capture agent 50/50 50/50 50/50 50/50 50/50 50/50 50/50 (capture agent-1/capture agent-2) Antioxidant(parts by mass) 3 3 3 3 3 3 3 Content of bromine in composition 30  20  40  30  30  30  30  (% by mass) Evaluation of Black foreign substance Good Good Good Good Good Good Good heat stability Discoloration Good Good Good Good Good Good Good Comparative Examples Examples 26 27 28 29 5 6 Styrene-based resin + 100  100  100  100  100  100  brominated polymer type flame retardant (parts by mass) Epoxy compound-1 (parts by mass) 10  10  10  10  — 10  Epoxy compound-2 (parts by mass) 5 5 5 5 — 5 Halogen capture agent-1 (parts by mass) 3 3 5 — 5 — Halogen capture agent-2 (parts by mass) 3 3 — 5 5 — Mass ratio of halogen capture agent 50/50 50/50 — — 50/50 — (capture agent-1/capture agent-2) Antioxidant(parts by mass) 1 5 3 3 3 3 Content of bromine in composition 30  30  30  30  30  30  (% by mass) Evaluation of Black foreign substance Good Good Good Good Poor Poor heat stability Discoloration Good Good Average Average Poor Poor

As shown in Table 1, it was found that, in the resin compositions of Examples 1 to 8 using the epoxy compound and the halogen capture agent in combination, the occurrence number of black foreign substances is reduced to 4 or less even when the resin compositions are heated at 220° C. for 60 minutes, compared with the resin compositions of Comparative Examples 1 and 2 using only one of the epoxy compound and the halogen capture agent, and the thermal stability of the brominated polymer type flame retardant in the resin composition is improved.

As shown in Table 2, it was found that, in the resin compositions of Examples 9 to 18 using the epoxy compound and the halogen capture agent in combination and using the dolomite-based compound and the hydrotalcite-based compound in combination as the halogen capture agent, the occurrence number of black foreign substances is reduced to 4 or less; the occurrence of discoloration is prevented; and the thermal stability of the brominated polymer type flame retardant in the resin composition is further improved.

Furthermore, as shown in Table 3, it was found that, in the resin compositions of Examples 28 and 29 using the epoxy compound, the halogen capture agent, and the antioxidant in combination, the occurrence of black foreign substances is prevented, and discoloration is also suppressed. Furthermore, it was found that, in the resin compositions of Examples 19 to 27 using the epoxy compound, the halogen capture agent, and the antioxidant in combination, and using the dolomite-based compound and the hydrotalcite-based compound in combination as the halogen capture agent, both the occurrence of black foreign substances and discoloration are prevent, and the thermal stability of the brominated polymer type flame retardant in the resin composition is highly improved. 

The invention claimed is:
 1. A flame-retardant resin composition comprising: a styrene-based resin; a brominated polymer-based flame retardant; an epoxy compound; an antioxidant; and a halogen capture agent for improving a thermal stability of the brominated polymer-based flame retardant, the halogen capture agent consisting of a dolomite-based compound and a hydrotalcite-based compound, wherein a content of bromine is 18 to 42% by mass, 4 to 25 parts by mass of the epoxy compound, 0.8 to 7 parts by mass of the antioxidant and 0.8 to 15 parts by mass of the halogen capture agent based on a total of 100 parts by mass of the styrene-based resin and the brominated polymer-based flame retardant are present, and the brominated polymer-based flame retardant has the following features (a) to (f): (a) the brominated polymer is a brominated styrene-butadiene block copolymer having butadiene and styrene as a monomer component; (b) a content of the styrene monomer in the copolymer before bromination is 5 to 90% by mass; (c) 1,2-butadiene is contained in the butadiene; (d) a weight average molecular weight (Mw) is 1000 or more; (e) a content of unbrominated nonaromatic double bonds determined by ¹H-NMR spectroscopy is less than 50% based on a content of nonaromatic double bonds of the copolymer before bromination; and (f) 5% weight reduction temperature obtained by thermogravimetric analysis (TGA) is 200° C. or higher.
 2. The flame-retardant resin composition according to claim 1, wherein a mass ratio of the dolomite-based compound to the hydrotalcite-based compound (dolomite-based compound/hydrotalcite-based compound) is 10/90 to 90/10.
 3. The flame-retardant resin composition according to claim 2, wherein the antioxidant is a phenol-based antioxidant.
 4. The flame-retardant resin composition according to claim 3, wherein the antioxidant is a hindered phenol-based antioxidant.
 5. The flame-retardant resin composition according to claim 1, wherein the antioxidant is a phenol-based antioxidant.
 6. The flame-retardant resin composition according to claim 5, wherein the antioxidant is a hindered phenol-based antioxidant.
 7. A flame-retardant resin molded article comprising the flame-retardant resin composition according to any one of claims 1, 2, 5, 6, 3 and
 4. 8. A flame-retardant resin molded article comprising the flame-retardant resin composition according to any one of claims 1, 2, 5, 6, 3 and 4, and a further styrene-based resin. 